ATM Jitter and Latency Measurements at DTU

These results come from a series of jitter and latency measurements on the ATM loopback connection from DTU/Lyngby to Aalborg University. The general setup of this connection is:

network setup

Each of the switches at DTU in Lyngby and Aalborg University (AAU) can be put into loopback mode, so that data sent from a work station at DTU in Lyngby return to Lyngby either after passing only through the local switch (Local Area ATM loopback) or after being transmitted to AAU and returning from the switch there (Wide Area ATM loopback). The Wide Area ATM connection from Lyngby to Aalborg passes through a TeleBit switch at UNI-C in Lyngby and continues via TeleDanmark's ATM network to a corresponding TeleBit switch in Aalborg, and from there to the ATM switch at the Department of Computer Science at AAU.

Latency is a measure of the time taken to transmit data, and is in the context of these experiments taken to be the time from when a sender transmits a quantity of data until the receiver receives them. Jitter is a measure of variation in transmission time, and is here expressed in terms of the width of the observed distribution of transmission times. Real-time applications and applications such as distributed shared memory often require a high degree of synchronism between activities in several computers, and therefore benefit from small latencies, while applications such as transmission of real-time video and audio demand low jitter in order to work satisfactorily. This work is related to current projects at DTU in these areas, such as the work going on on Interactive Distributed Multimedia.

In these experiments we have tried to investigate what conditions have to be fulfilled in order to achieve low latency and jitter in computer systems connected by an ATM network. The factors considered potentially to be of interest are:

The experiments which have been designed to illustrate the effects of these factors fall into two parts:
  1. Jitter measurements
  2. Latency measurements

The results shown on these Web pages are typical, but are not an exhaustive list of the experiments carried out. For more details, contact the authors.

Thomas Dibbern
Updated 14 November 1997 by Robin Sharp